The Westminster Collection is a company that provides unique collectible stamps and coins. They are well known in the UK but those of us on the US might not be familiar with them, which is a shame because they have beautiful items.
On September 9, 2019, they will add Harry Potter to their site. I don't yet know what they will reveal but my guess is that they will be coins, and this guess is based on the image that they've created on their "Coming Soon" page. You can sign up to be notified on the 9th for whatever magical items are coming by clicking here.
FYI, the link I provided above is for their UK site and they don't ship to the US. There is a US site but there isn't anything on that version of their site regarding Harry Potter so this might just be exclusive to residents of the United Kingdom.